Date of Award

1995

Document Type

Thesis

Publisher

Edith Cowan University

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Science, Technology and Engineering

First Supervisor

Dr Ian Bennett

Second Supervisor

Danielle Eyre

Third Supervisor

Dr Mary Bryce

Abstract

The use of eucalypts for plantation timber and pulp is becoming increasingly important, as are eucalypts that are resistant to disease and insect herbivory. Where clones with desirable traits have been selected, it is important that these genotypes are preserved. Micropropagation of some eucalypts, and Eucalyptus marginata in particular, can be difficult possibly due to the currently used basal medium of Murashige and Skoog (M&S)(I 962). By examining the nitrogen utilisation and the effects of medium pH of this species, it may be possible to improve general micropropagation protocol. Six clones of the species E. marginata were obtained as shoot cultures. The pH of M&S medium was successfully buffered using 2-(Nmorpholino) ethanesulfonic acid (MES) for both shoot multiplication and root induction. This did not result in any growth increase. Increased growth was achieved when shoots were grown on buffered medium that contained less nitrogen than M&S (20 mM and 40 mM) and the nitrogen was supplied solely as nitrate. Shoots grown on buffered (I 0 mM MES) root induction medium produced more roots than those grown on unbuffered medium. Root induction medium containing nitrate as the sole source produced more roots than did media with ammonium and nitrates or solely ammonium. These results suggest that E. marginata prefers nitrate to ammonium as a nitrogen source, and that the current level of total nitrogen may be too high. The pH of culture medium for both shoot multiplication and root induction remained constant with nitrate as the sole nitrogen source but fell significantly when ammonium was the sole source. This occurred even when MES was supplied at I 0 mM. Increasing the level of MES to 20 mM in the medium resulted in less shoot growth. When different clones were subjected to the same treatments, significant differences in shoot growth and percentage of rooting between clones were observed, highlighting the genetic variability within the species.

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